Over the last few decades, the electronics industry has undergone a revolution by the use of semiconductor technology to fabricate small, highly integrated electronic devices. The most common semiconductor technology presently used is silicon-based. A large variety of semiconductor devices have been manufactured having various applications in numerous disciplines. Such silicon-based semiconductor devices often include metal-oxide-semiconductor (MOS) transistors, complimentary MOS (CMOS) transistors, bipolar transistors, bipolar CMOS (BiCMOS) transistors, etc.
Each of these semiconductor devices generally include a semiconductor substrate on which a number of active devices are formed. The particular structure of a given active device can vary between device types. For example, in MOS transistors, an active device generally includes source and drain regions and a gate electrode which modulates current between the source and drain regions. In bipolar transistors, an active device generally includes a base, a collector, and an emitter.
Semiconductor devices, like the ones mentioned above, are used in large numbers to construct most modern electronic devices. As a larger number of such devices are integrated into a single silicon wafer, improved performance and capabilities of electronic devices can be achieved. In order to increase the number of semiconductor devices which may be formed on a given surface area of a substrate, the semiconductor devices must be scaled down (i.e., made smaller). This is accomplished by reducing the lateral and vertical dimensions of the device structure.
One important step in the formation of semiconductors is the process of forming isolation regions, i.e., regions in the substrate which are used to electrically isolate adjacent active devices. Two common techniques for isolating active devices on a semiconductor substrate are LOCOS (for LOCal Oxidation of Silicon) isolation and trench isolation. Trench isolation techniques, and many LOCOS isolation techniques, generally involve the formation of a trench in the substrate. In most cases, an oxide layer is grown in the trench to form at least part of the isolation region. In trench isolation, a second layer of oxide may be deposited over the grown oxide layer to completely fill the trench.
The isolation region resulting from trench isolation techniques (and those LOCOS isolation techniques which involve trenches) is often associated with a number of limitations. For example, the sidewalls of the isolation region are often etched away during subsequent processing steps, resulting in voids at the edges of the trench. Such voids impact device parameters by, for example, increasing the non-uniformity of those parameters. This problem becomes more significant as devices become smaller and trenches become shallower. A more detailed discussion of LOCOS and trench isolation techniques can be found in S. Wolf, Silicon Processing For The VLSI Era, Vol. 2: Processing Integration, Chap. 2, pp. 28-58, 1990.